This invention relates to providing a side seal between a plastic closure and a bottle and, more specifically, to providing a side seal by ironing a marginal portion of a liner adjacent the liner edge while assembling a closure with a bottle.
Plastic closures have become increasingly popular for use in a wide variety of packaging applications because of certain inherent characteristics of plastic materials. For example, plastics demonstrate relatively good corrosion resistance in diverse environments; plastics are capable of being molded into intricate shapes; and plastic closures can be made to offer aesthetic appeal to the consumer.
A potentially very large market for plastic closures which has developed only minimal usage to date, however, is in packaging carbonated beverages. Carbonated beverages packaged in glass or plastic bottles are, for the most part, confined within the bottle by a metal closure having a plastic liner therein. An early patent, Hammer U.S. Pat. No. 910,128, describes one type of a metal closure having a packing disc therein which provides both a side seal and top seal when applied to a threaded container. The closure described in Hammer is preformed before assembly with the container; that is, the structure of the closure is completely formed prior to assembling the closure with the container. During application of the closure, a peripheral portion of the packing disc is bent around the outer side of the mouth of the container and compressed against the container wall to provide a side seal. The end panel compresses the disc against the top of the mouth of the container to also effect a top seal.
Further developments of metal closures for sealing carbonated beverages are described in patents such as Osborne et al U.S. Pat. No. 3,303,955 and Hadley U.S. Pat. No. 3,868,038. In these patents a metal closure blank having a liner laminated to the end wall thereof is provided and the closure is engaged with a threaded bottle by deforming the skirt with a roller to conform to the bottle thread. Prior to rolling the thread in the skirt, a pressure block adapted to deform an end wall portion of the blank is axially applied to the blank and deforms a peripheral portion of the end wall to bend it around the mouth of the closure and thus compress the liner against both the top of the bottle mouth and the outer surface adjacent the mouth to effect both a top seal and side seal.
Plastic closures have not been widely used to package carbonated beverages primarily because of the problem of maintaining an effective seal between the closure and the container due to the internal pressure within the sealed container from gas escaping from the carbonated beverage.
When plastic materials are subjected to a stress over any extended period of time, they have a tendency to creep or cold flow. This tendency is exacerbated if the plastic is exposed to elevated temperatures. In packaging carbonated beverages, therefore, the shelf life of a beverage sealed in a bottle with a plastic closure is of greater concern than if the beverage is packaged by using a metal closure to effect a seal. Manufacturing tolerances of commercial bottles have also presented problems in the use of plastic closures. Relatively speaking, the manufacturing tolerances in making a conventional glass bottle are large, and fabrication of a molded plastic closure to accommodate the wide range of diameters encountered in a given bottle size and still maintain an effective seal has been a major problem for plastic closure manufacturers.
To solve these problems a number of solutions have been proposed. For example, Plunkett U.S. Pat. No. 3,055,526, Healy U.S. Pat. No. 3,160,303 and Gibson U.S. Pat. No. 3,232,470 feature linerless closure structures which rely upon a compressive seal on the rim face of the container. Mumford U.S. Pat. No. 4,322,011 provides a side sealing rib on the skirt wall of the closure in addition to a top seal to improve the seal reliability. Another approach has been to provide a plug-type structure which provides a seal, at least in part, from the interaction between the plug and the inner surface of the container neck. Examples of closures of this kind are described in Grussen U.S. Pat. No. 3,462,035 and Salminen U.S. Pat. No. 3,209,934.
A plastic cap having a separate liner contained therein is described in Evans et al U.S. Pat. No. 3,480,170 and sealing is effected simply by compressing the liner which is positioned adjacent the under surface of the top wall of the cap against the container mouth.
Primarily because of the loss of an effective seal after packaging, plastic carbonated beverage closures have not gained widespread acceptance in the industry in spite of the many efforts to develop a plastic closure for such use.
Accordingly, a plastic beverage closure is desired that can be used to package carbonated beverages in either a glass or plastic bottle and retain an effective seal over extended periods of time.